Anhydrous actinide trichlorides such as plutonium trichloride and neptunium trichloride are important starting materials for chemical synthesis. Plutonium trichloride can be prepared by a number of methods such as the reaction of either carbon tetrachloride or phosgene with plutonium oxide, the reaction of either hydrogen chloride or phosgene with plutonium oxalate, the reaction of plutonium metal with chlorine, the reaction of plutonium hydride with hydrogen chloride, or the reaction of a mixture of ammonium chloride and liquid hydrogen chloride with plutonium oxide. While such reactions are all reasonably efficient in producing plutonium trichloride, they suffer from disadvantages such as poor waste minimization and greater radiation exposures to personnel. In addition, when plutonium oxide is used, it must be initially prepared, usually by calcining an oxalate which itself is generally first precipitated from an aqueous solution. Similarly, the use of plutonium hydride or plutonium metal requires that the metal be initially produced. In these cases, the end product of a first multi-step process is used to feed another multi-step process.
One desirable route in the preparation of anhydrous plutonium trichloride would be to use a solution of plutonium in hydrochloric acid. It is previously known that evaporation of such plutonium solutions can yield plutonium chloride hydrate and that the anhydrous product can then be obtained by heating the hydrate in a stream of dry hydrogen chloride. While this method is useful, such a process is generally unsuitable for preparations of the anhydrous product because of the quantities of gas needed and the added difficulties of drying, recycling and/or scrubbing the hydrated HCl by-product. Moreover, attempts to obtain the anhydrous material directly from the aqueous solution simply by evaporation and further heating suffer from significant formation of plutonium oxychloride occurs upon dehydration.
Thionyl chloride, SOCl.sub.2, has long been known to produce anhydrous chlorides from many metal hydrates. It has also been used in organic chemistry as a coreactant to remove water from a reaction mixture. The use of thionyl chloride as a dehydrating agent for preparation of anhydrous inorganic chlorides is described by Freeman et al. in J. Inorg. Nucl. Chem., vol. 7, pp.224-227 (1958). However, Freeman et al. report that the process was not applicable to plutonium trichloride. This is in contrast to their work with other chlorides such as thorium, copper, magnesium, or iron, and numerous lanthanide metal chlorides.
Surprisingly, the present inventors have now discovered that thionyl chloride can be used as a dehydrating agent for the conversion of plutonium trichloride hydrate to anhydrous plutonium trichloride, such a process being further applicable to trivalent neptunium trichloride as well.
Accordingly, it is an object of this invention to provide a process of converting plutonium trichloride hydrate to anhydrous plutonium trichloride.
It is a further object of the invention to provide a process of converting neptunium trichloride hydrate to anhydrous neptunium trichloride.